After six months of contentious labor negotiations that resulted in two strikes, the Bay Area Rapid Transit District (BART) finalized an agreement with unions last month that put an end to the dispute.

Or not.

Last Friday, BART officials announced that they had mistakenly agreed to a provision in the four-year contract that they had no intention of including and wanted a do-over. They blamed a “temporary employee” for the error. The union said a deal is a deal and ridiculed the agency’s contention that it had made an honest mistake.

“It’s a further demonstration of a combination of incompetence and no real desire to get an agreement,” SEIU Local 1021 Executive Director Peter Castelli told the Associated Press. “I've been bargaining union contracts for over 25 years, and I have never seen anything like this happen, ever.”

At issue is a clause that obligates BART to pay for up to the first six weeks of family medical leave taken by the 2,300 union members covered under the agreement. Until now, workers could take 12 weeks of leave but had to use vacation time, sick days or other accrued time. BART said the change would cost the agency $44.2 million over four years and had been soundly rejected during negotiations.

The agency said it was an unintentional error and wanted to return to the bargaining table to discuss it. “Mistakes happen in the business world and in life every day,” BART said in a statement. “That is not an excuse—it is just a fact. During a final review process, the mistake was caught by staff before the BART Board voted on the contract and it will be fully vetted before the contract is considered.”

Union leaders agreed the change had been discussed but said both sides tentatively accepted the new terms in July and there is no reason to discuss it further. The unions said BART management was vastly overestimating the cost of the provision, and put it at $1.4 million a year. Antonette Bryant, president of Amalgamated Transit Union Local 1555, called the amount “lint in their pocket.”

Members of the SEIU and Amalgamated Transit local have already ratified the contract.

BART and union officials met on Monday to discuss just how much money is really at stake because of the disagreement, but there was no attempt at a renegotiation. The BART board of directors is scheduled to vote on final acceptance of the agreement on Thursday.